#define _CRT_SECURE_NO_WARNINGS 1;

double add(double x, double y) {
	return x + y;
}
double sub(double x, double y) {
	return x - y;
}
double mult(double x, double y) {
	return x * y;
}
double div(double x, double y) {
	if (y == 0.0) return;
	return x / y;
}